1. Field of the Invention
The present invention relates to a method for afforestation and to a structure used for the method. This method is designed for afforestation of deserts, dunes, and sands suffering extreme droughtiness due to a larger amount of evaporation compared with rainfall.
With this method, one will be able to grow plants and vegetables in deserts, dunes, and sands, thereby making them fertile.
2. Description of the Related Art
There have been proposed various methods for afforestation of extremely droughty lands, such as deserts, dunes, and sands, where evaporation exceeds rainfall.
For example, Japanese Patent Laid-open No. 60613/1989 discloses a method for afforestation of deserts. This method consists of driving sheathing boards into the land for planting at its boarder,digging out soil in the surrounded area, forming an impervious layer on the bottom and wall of the hole, placing watering pipes and composting soil in the hole for forming a vegetation layer, seeding in the vegetation layer, covering the surface of the vegetation layer with a breathable protective film and a shading film, and allowing germination.
Also, Japanese Patent Laid-open No. 104741/1992 discloses a method for afforestation of arid land. This method consists of burying boards in soil of arid land, thereby forming a partitioned part surrounded by the buried boards, mixing the soil in the partitioned part with a water holding material in a certain ratio, planting trees in the partitioned part, tightly closing the top of the partitioned part after planting, and watering the partitioned part until the planted trees are rooted deep to ground water.
Japanese Patent Laid-open No. 197626/1994 discloses a method for afforestation of deserts. This method consists of forming partly in sand a substance or structure having both water retentivity and air permeability, and then seeding or planting in the upper part of the substance or structure.
In addition, Japanese Patent Laid-open No. 49722/1985 discloses a method for vegetation. This method consists of making holes at certain intervals in scree, desert, coastal sand dune, or slope, and setting in each hole a bottomless cylindrical body containing a nursery plant therein, said cylindrical body being reticulate, perforated, or of fibrous structure to impart water permeability and water absorptivity through capillary action and to permit lateral roots to grow through it.
Of the above-mentioned four Japanese patents, the first and second are intended to create in land a water holding part suitable for plant growth, thereby growing plants in such a part. Therefore, afforestation in this manner takes a great deal of labor and expenses to form the vegetation layer. In addition, planted trees need innegligible labor and expenses for watering. Thus, the methods disclosed therein are not practicable in a vast desert.
By contrast, the third (which employs a water-retentive and air-permeable cylindrical structure) is advantageous over the first and second because it permits the vegetation layer to be formed easily and economically. However, the substance or structure does not retain water necessary for plant growth in desert where the daytime temperature is 70-80xc2x0 C. or the average temperature is 40-50xc2x0 C. even in the ground 30-50 cm deep. In such an environment, water evaporates easily due to ground heat, and hence there is an acute need for watering. The method of the third reference is effective in areas of comparatively moderate climate but is not effective in arid land (such as desert) where the daytime temperature is high and the water evaporation is rapid.
The method of vegetation disclosed in the fourth reference seems effective in that the planted trees can have root downward; however, like the method of the third reference, it will not work effectively in arid land such as desert.
The present invention was completed in view of the foregoing. It is an object of the present invention to provide a method for afforestation of sands and the like, said method permitting one to grow easily trees and vegetables in tropical arid land where the daytime temperature is high and the water evaporation is rapid. It is another object of the present invention to provide a structure to be used for said method.
The first aspect of the present invention resides in a method for afforestation of sands and the like, the method comprising digging the ground to form a vertical hole with a prescribed sectional area and depth, fitting an outer cylindrical body into the hole, filling the outer cylindrical body with soil containing a water-holding material, making a hole with a prescribed sectional area and depth at the center of the soil in the outer cylindrical body, placing in the hole an inner cylindrical body with a prescribed sectional area and length which is filled with soil containing a water-holding material and has a large number of vent holes in its lower section, watering the soil in the outer cylindrical body and the inner cylindrical body so that the water-holding material absorbs sufficient water, sowing a seed or transplanting a nursery tree in the soil in the inner cylindrical body, and growing the plant, with the outer cylindrical body preventing water from escaping from the soil therein, and the soil in the outer cylindrical body isolating the soil in the inner cylindrical body from the ground heat, thereby keeping the soil for vegetation in a cool and wet condition.
The second aspect of the present invention resides in a structure used for afforestation of sands and the like, the structure comprising a heat-insulating outer cylindrical body with a prescribed sectional area and length, and a heat- insulating inner cylindrical body with a prescribed sectional area and length, the inner cylindrical body being filled with soil for vegetation containing a water-holding material and being inserted into a hole formed at the center of the outer cylindrical body.
The third aspect of the present invention resides in a structure used for afforestation of sands and the like, the structure comprising a heat-insulating outer cylindrical body with a prescribed sectional area and length, which is filled with soil containing a water-holding material such that a hole with a prescribed sectional area and length is left at the center of the soil, and a heat-insulating inner cylindrical body with a prescribed sectional area and length, the inner cylindrical body being filled with soil for vegetation containing a water-holding material and being inserted into the hole formed at the center of the outer cylindrical body.